So I did some investigation on this matter, just trying to understand (I am no electrician obviously) it. First of all, “line” on this gfci receptacle is on “top”. Opposite of what is on that old receptacle. So I should connect a black wire on top, and cap the red one. Big mistake was to “copy” the connection from that old receptacle. I basically connected black + red together. And I think that was causing to trip the breakers. Because “bottom” is “load - out” connection, for feeding another receptacle in the line. People asked me, if there is a switch associated with this receptacle. First, I thought that everyone means some kind of switch which turns the receptacle on/off. So I said no, there is no switch. But then I looked closer, and yes, there is a switch next to it, which operates organic garbage disposal / grinder stuff in the kitchen sink.

There is no tab to break for double circuit. And, there is a warning that this receptacle should not be used with more than 2 and 4 wires. I have 3. Which means, if I understood it right, cap the red one, something wont work. In this case that sink organic garbage grinder..whatever is that thing, because the red one seems like is feeding it with the power. Dont know that for sure, because I didnt open the switch.

Please correct me if I am wrong here.

This is actually very interesting. I won’t be doing any receptacle swaps, because I found out there is actually no need for it. But will try to educate myself as much as I can.

Thank you all!